AAF International has developed a gas turbine (GT) inlet cooling system which provides fast response to the changing dynamics of gas turbine power generation. High-capacity rotary atomisers on the dirty air side of filters, combined with a control system to finetune the downstream temperature, are key features of its new InstaKool system.
Performance of gas turbines depends on air flow through the compressor to the combustion section. As the temperature of incoming ambient air increases, its density drops as does the mass flow through the turbine. Consequentially, the gas turbine output decreases and the fuel rate increases. Hence, inlet cooling is vital to keep performance levels up.
Cooling of inlet air can be achieved by either adiabatic cooling, which interfaces a water supply with the incoming air. Sensible energy is given up by the air, providing latent heat of evaporation until the air reaches new equilibrium. No heat is removed from the system, the air enthalpy remains constant.
Chilled water cooling, on the other hand, removes heat from the air via by circulating water in coils in a closed loop. In turn the chiller disperses the heat removed from the air via a condenser by a cooling tower or cooling fans. Depressing air temperature below its dew point will produce condensate on the coils.
For turbines with highly variable loads, adiabatic cooling allows to increase output and reduce heat rate in order to meet peak demand quickly. Standard methods of adiabatic cooling have been media evaporative cooling and high pressure fogging – both systems are located downstream of inlet filters.
Technicalities of InstaKool
InstaKool, a new inlet cooling system developed by AAF International, comprises of high capacity rotary atomisers located upstream of the final filters, with a rigorous control system which ensures that filter differential pressure is not compromised.
By the introducing a fine mist into the air stream, ahead of the final filters, InstaKool provides adiabatic cooling. The mist delivery device is a high capacity rotary atomiser which only requires low pressure water. Varying the atomiser water flow rate does not affect the water droplet particle size distribution, which allows the system to be finely controlled from zero to 100% water flow.
Designed to provide a fast response to cooling demands, modular control panels are located adjacent to the filter house, providing 200 Watts of power to each atomiser. Cascade control of differential pressure, followed by relative humidity protects filters from differential pressure excursions. This strategy enables the gas turbine operator to trim output by adjusting the downstream temperature between ambient and the reduced temperature at 80% relative humidity (see graph).